linux-kernel - Re: [PATCH v5] regulator: core: Resolve supply name earlier to prevent double-init

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Date:   Fri, 17 Feb 2023 16:05:52 -0800
From:   Saravana Kannan <saravanak@...gle.com>
To:     Christian Kohlschütter 
        <christian@...lschutter.com>
Cc:     Mark Brown <broonie@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Heiko Stübner <heiko@...ech.de>,
        lgirdwood@...il.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-mmc@...r.kernel.org,
        linux-rockchip@...ts.infradead.org, m.reichl@...etechno.de,
        robin.murphy@....com, vincent.legoll@...il.com, wens@...nel.org
Subject: Re: [PATCH v5] regulator: core: Resolve supply name earlier to
 prevent double-init

On Fri, Feb 17, 2023 at 4:01 PM Christian Kohlschütter
<christian@...lschutter.com> wrote:
>
> On 18. Feb 2023, at 00:46, Saravana Kannan <saravanak@...gle.com> wrote:
> >
> > On Fri, Feb 17, 2023 at 3:33 PM Christian Kohlschütter
> > <christian@...lschutter.com> wrote:
> >>
> >> On 18. Feb 2023, at 00:22, Saravana Kannan <saravanak@...gle.com> wrote:
> >>>
> >>> On Thu, Aug 25, 2022 at 2:28 PM Christian Kohlschütter
> >>> <christian@...lschutter.com> wrote:
> >>>>
> >>>> Previously, an unresolved regulator supply reference upon calling
> >>>> regulator_register on an always-on or boot-on regulator caused
> >>>> set_machine_constraints to be called twice.
> >>>>
> >>>> This in turn may initialize the regulator twice, leading to voltage
> >>>> glitches that are timing-dependent. A simple, unrelated configuration
> >>>> change may be enough to hide this problem, only to be surfaced by
> >>>> chance.
> >>>
> >>> In your case, can you elaborate which part of the constraints/init
> >>> twice caused the issue?
> >>>
> >>> I'm trying to simplify some of the supply resolving code and I'm
> >>> trying to not break your use case.
> >>>
> >>> -Saravana
> >>
> >> Here's a write-up of my use case, and how we got to the solution:
> >> https://kohlschuetter.github.io/blog/posts/2022/10/28/linux-nanopi-r4s/
> >
> > I did read the write up before I sent my request. I'm asking for
> > specifics on which functions in the set_machine_constraints() was
> > causing the issue. And it's also a bit unclear to me if the issue was
> > with having stuff called twice on the alway-on regulator or the
> > supply.
> >
> > -Saravana
>
> I'm afraid I cannot give a more detailed answer than what's in the write up and the previous discussion on this mailing list; I thought it's pretty detailed already.

Well, I do my best not to break your use case with whatever info you
are willing to provide. We'll figure it out one way or another I
suppose.

> However, it should be relatively straightforward to reproduce the issue.

If one has the hardware. Which I don't.

-Saravana